1. Field of the Invention
This invention relates to a method of manufacturing photolithographic features which have high aspect ratios. This method is applicable to manufacturing devices such as recording heads for disk drives and semiconductor integrated circuits.
2. Description of the Background Art
Devices which are made with photolithographic processes include articles such as recording heads for disk drives and integrated circuits for a variety of applications. In general there is a trend to make such devices smaller and smaller. The important dimensions of such devices can include for example the track widths of recording heads and conductor widths for integrated circuits.
The conventional photolithographic processes of manufacturing these small features involve first forming a layer of photo resist on a substrate such as metal or silicon. Then a pattern is created in the resist layer by first exposing through a patterned mask with the proper light for that particular resist and then chemically dissolving away the exposed portions of the resist to expose the underlying substrate. The actual structure in the final device is then usually constructed by plating or otherwise building the features onto the substrate. After the feature has been built, the remaining resist layer is removed. This conventional approach is appropriate when the width of the desired features is relatively large compared to the depth or thickness of the resist; or correspondingly, when the width of the features is large relative to the height of the feature. The aspect ratio of a feature is defined as the height of a feature divided by the width. For example, a recording head for very high density applications would have a very narrow track width and the height of the write pole would be large compared to the track width.
When manufacturing high aspect features conventional photolithographic processes have serious shortcomings. Among these shortcomings are lack of precise definition of the desired template in the resist and undercutting when the resist is chemically treated. Both of these shortcomings limit the ability of conventional methods to achieve high aspect ratio features.
An improvement in the conventional processes of achieving high aspect ratio features has been the use of an image transfer process. In this process a thin adhesion layer, typically containing a tantalum rich material is placed on the substrate to provide improved adhesion for the resist layer. A thin top layer of a silicon rich or tantalum rich material is placed on top of the resist layer, and a pattern is created in this top layer. Then, instead of using photolithography with a wet chemical process to dissolve the underlying resist layer, an oxygen based reactive ion etch (RIE) is used to create the template in the resist layer. This method has the advantage of creating more sharply defined walls in the resist template (e.g. little undercutting). However, this approach has at least two noteworthy shortcomings. One, the adhesion layer material which is removed during the RIE process tends to deposit on the walls of the photoresist template. Furthermore, it is difficult to completely remove the remaining adhesion layer without damaging or undesirably altering the patterned substrate.
There is a need for a process which has an effective adhesion layer between the substrate and resist which protects the substrate and is subsequently easy to remove.
The present invention is a photolithographic process which includes a step of forming an effective etch barrier for an oxygen RIE process. The process results in improved protection of the substrate and more sharply defined goemetrical features. The steps of the process of the present invention include first placing a silicon rich thin layer on the substrate using a low energy deposition. A thin diamond like carbon (DLC) layer is then placed on the silicon rich layer. Relatively thick resist is then placed on the DLC. Finally the image transfer layers comprising a silicon rich or tantalum rich layer and an additional resist layer which is relatively thin are placed on the thicker resist. The DLC layer provides good adhesion with the resist. The silicon rich material on the substrate is the etch barrier which protects the substrate during the oxygen RIE. The silicon rich material is subsequently removed with a fluorine based RIE without damage to the substrate and with minimal redeposition on the walls of the features in the resist layer. These steps allow high aspect ratio photolithographic features to be constructed.